Elimination of maternal to child transmission of HIV will require identification of effective, feasible, cost- effective and scalable ways to engage and retain HIV-infected pregnant women and their infants in prevention of mother to child transmission (PMTCT) and HIV care and treatment programs in a seamless continuum across the entire PMTCT cascade. We propose Mother Infant Retention for Health (MIR4Health), an innovative implementation science study focused on identifying an effective multicomponent strategy to improve linkage and retention of newly identified HIV infected pregnant women accessing mother child health services in Nyzana Province, Kenya. The study is a randomized trial to compare the effectiveness of a novel strategy using Active Patient Follow-Up (APFU) to engage and retain newly identified pregnant HIV-infected women and their infants in care compared to the current standard of care (SOC) for the retention of the women and their exposed infants postpartum. The proposed APFU includes a package of evidence-based interventions including health education, provision of phone and short message service appointment reminders, active tracking of patients for linkage and retention, and individualized retention and adherence support. The primary aim is to evaluate the effectiveness of APFU plus SOC compared to SOC on the combined outcome of retention of both mother and infant at 6 months postpartum. In addition, we will examine the effectiveness of the intervention on other critical outcomes including maternal attendance at 2nd antenatal visit; changes in CD4+ cell count and HIV RNA viral load; Polymerase Chain Reaction (PCR) testing of HIV-exposed infants at 6 weeks; and adherence by women and infant to prescribed antiretroviral regimens. MIR4Health is distinguished by several innovations including the recognition that the newly identified HIV-infected pregnant woman especially vulnerable to poor retention within PMTCT and that both mother and child must be retained in care to ensure optimal health outcomes. The use of a feasible, pragmatic approach that addresses known barriers, builds on evidence based interventions and is potential to be scaled-up if successful can contribute to Kenya's efforts towards elimination of new pediatric infections and to safeguard maternal health.